Daniel B. Danielidis

SEXUAL REPRODUCTION, MATING SYSTEM, AND PROTOPLAST DYNAMICS OF SEMINAVIS (BACILLARIOPHYCEAE)1

Cell division, the mating system, and auxosporulation were studied in the marine epipelic diatom Seminavis cf. robusta Danielidis & D. G. Mann. The interphase protoplast contains two girdle‐appressed chloroplasts, each with an elongate bar‐like pyrenoid, and also a central nucleus, located in a bridge between two vacuoles. Before cell division, the chloroplasts divide transversely and translocate onto the valves. The nucleus relocates to the ventral side for mitosis. After cytokinesis and valve formation, the chloroplasts move back to the girdle, showing a constant clockwise movement relative to the epitheca of the daughter cell. Seminavis cf. robusta is dioecious, and sexual reproduction is possible once cells are less than 50 μm. In crosses of compatible clones, gametangia pair laterally, without the formation of a copulation envelope, and produce two gametes apiece. The intensity of sexualization increases as cells reduce further in size below the 50‐μm threshold. At plasmogamy, the gametangia dehisce fully and the gametes, which were morphologically and behaviorally isogamous, fuse in the space between the gametangial thecae. The auxospore forms a transverse and longitudinal perizonium. After expansion is complete, there is an unequal contraction of the protoplast within the perizonium, creating the asymmetrical shape of the vegetative cell. Apart from this last feature, almost all characteristics exhibited by the live cell and auxospores of Seminavis agree with what is found in Navicula sensu stricto, supporting the classification of both in the Naviculaceae. Haploid parthenogenesis and polyploid auxospores were found, lending support to the view that change in ploidy may be a significant mechanism in diatom evolution.

The systematics of Seminavis (Bacillariophyta) : the lost identities of Amphora angusta, A. ventricosa and A. macilenta

Amphora angusta Gregory, Amphora ventricosa Gregory and Amphora macilenta Gregory have been misunderstood for the last 140 years. Gregory described these species from sublittoral sediments off the west coast of Scotland. Although the illustrations were excellent for their time (1857), it is impossible to be confident of identification using Gregorys paper, and subsequent authors have created such confusion that records of these taxa must be regarded as untrustworthy unless backed by photographic evidence. In this paper, the first to describe in detail the recently established genus Seminavis, we show that A. angusta is in fact a species of Amphora Ehrenberg, whereas A. ventricosa sensu Gregory represents two independent species of the genus Seminavis D. G. Mann, namely Seminavis ventricosa (Gregory) Garcia-Baptista (non S. ventricosa sensu Garcia-Baptista 1993) and Seminavis arranensis Danielidis & D. G. Mann, sp. nov. The form usually known as A. ventricosa is neither of these and requires a new name, Seminavis robusta Danielidis & D. G. Mann, sp. nov. The long forgotten and misclassified species A. macilenta Gregory is shown to be yet another Seminavis species, requiring a new combination as S. macilenta (Gregory) Danielidis & D. G. Mann, comb. nov.; contrary to previous claims, it is separate from A. ergadensis Gregory, which is a true Amphora. Valve and girdle ultrastructure, plastid arrangement and auxosporulation are described for Seminavis and resemble those in the Naviculaceae sensu stricto.

Limnological survey of Lake Amvrakia, western Greece

Limnological characteristics of lake Amvrakia, a deep warm monomictic and sulphate lake in western Greece, are presented. A set of physical and chemical variables were monitored for one year cycle (October 1988–September 1989). Phytoplankton community structure and biomass are given for the entire depth of the water column. The trophic status of the lake is compared to that of other temperate and tropical lakes.

Distribution survey of Cyanobacteria in three Greek caves of Peloponnese

Caves and hypogean environments host various phototrophic microorganisms, with Cyanobacteria constituting the major group. The spatial and temporal distribution of Cyanobacteria (156 taxa in total) from three Greek caves, located in the limestone arc of Peloponnese and differing in morphology, was studied. The community patterns in different ecological niches were analyzed in relation to environmental parameters (Photosynthetically Active Radiation, Temperature, and Relative Humidity). Cyanobacterial communities were found to thrive in patchy biofilms and showed known protective strategies against desiccation and irradiation. The nMDS analysis of the cumulative seasonal samples per sampling site showed no general pattern of distribution, with a clear differentiation of cyanobacterial communities among the three caves. Only in the typical cave ‘Kastria’, cyanobacterial taxa showed growth habits in accordance with the gradient of light from entrance inwards.

UV effects on invertebrate and diatom assemblages of Greece.

The effects of solar radiation (PAR, UVA, UVB) on the productivity and structure of diatom and invertebrate assemblages were assessed during primary succession on artificial substrate near a rocky shore of the Saronikos Gulf, Greece. Three light treatments were performed (PAR, PAR+UVA, and PAR+UVA+UVB) at 0.5, 1.0 and 1.5 m of depth. Pennate diatoms were the major component of the developing periphytic communities during the study period. Exposure to solar UVB initially reduced the biomass and altered the structure of the diatom assemblages. The highest biomass of diatom assemblages was observed under PAR (49.2 g/m2). This value was significantly higher than the biomass of assemblages growing under PAR+UVA+UVB, but not significantly different compared to the biomass of assemblages exposed to PAR+UVA. These differences, however, did not persist at later stages. The most abundant invertebrate groups present were Polychaetes and Crustaceans. Solar UVB did not have significant effects on invertebrate biomass. Analysis of the invertebrate assemblage structure revealed time-course differences but no clear trends among the different treatments.

NEW SPECIES AND NEW COMBINATIONS IN THE GENUS SEMINAVIS (BACILLARIOPHYTA)

A previous study, leading to the redefinition of Seminavis ventricosa (Gregory) Garcia-Baptista and some related taxa, made it clear that a considerable number of species exist within Seminavis D.G. Mann. Many species are still classified under Amphora Ehrenberg, although they clearly share common morphological features with Seminavis. Some of these species are described as new or transferred here, whereas others are only mentioned because of insufficient evidence, lack of original material, or poor documentation, so that taxonomic changes would be unwise at present. The species S. basilica Danielidis sp. nov., S. heidenii D.G. Mann sp. nov., S. strigosa (Hustedt) Danielidis & Economou-Amilli comb, nov., S. latior (A. Schmidt) Danielidis & D.G. Mann comb, et stat. nov., and S. obtusiuscula (Grunow) Danielidis & D.G. Mann comb. nov. all share the characteristic valve shape, areola structure and raphe constraction of typical Seminavis. Furthermore, in those species where fresh material was available, two plate-like, girdle-appressed chloroplasts were evident, as in other Seminavis and in almost all members of the Naviculaceae Kützing emend. D.G. Mann. The identity of S. cymbelloides (Grunow) D.G. Mann is discussed, although original material has not been available to us and may not exist. Lectotypes for A. angusta var. angustissima Van Heurck, A. diducta A. Schmidt, S. latior (A. Schmidt) Danielidis & D. G. Mann, and S. obtusiuscula (Grunow) Danielidis & D.G. Mann are also designated.

A niche-based modeling approach to phytoplankton community assembly rules.

Six niche-based models proposed by Tokeshi, based on different assumptions of resource allocation by species, were fitted on phytoplankton relative abundance distributions, and potential environmental and biotic factors supporting the applicability of the fitted models were discussed. Overall 16 assemblages corresponding to different sampling times, various environmental conditions, and resource regimes within a year were fitted to the models. Phytoplankton biovolume was used as a measure of abundance, and a randomization test was applied to compare the model fit to the field data. The majority of the phytoplankton assemblages (11 of 16) were successfully described by the Random Fraction model, which is based on the theoretical assumption that resource is apportioned by the species in a random way. Only a few assemblages (three of 16), characterized by extremes in resource availability or disturbance, were not fitted by any of the models. The Random Fraction model in particular was rejected due to a steep slope during the first ranks, while the rest of the distribution remained relatively even, providing further evidence of resilience in phytoplankton communities. Although larger cells seem to have the potential to develop higher biomass, it seems that other factors, including the surface-to-volume ratio, counterbalance this advantage, resulting in a random-like behaviour in resource acquisition by phytoplankton, irrespective of cell size or species identity.

Limnological survey of the warm monomictic lake Trichonis (central western Greece); I. The physical and chemical environment

The physical and chemical status of Trichonis – the largestanddeepest natural lake in Greece – is examined over two annualcycles (1985–86 and 1988–89). A correlation between lakenutrientpatterns and phytoplankton biomass is attempted. Limnologicalfeatures are compared with data from other warm and temperatelakes.With regard to its thermal regime, Trichonis is classified asawarm monomictic lake. The lakes stratification pattern andannualheat budget resemble those of other temperate lakes. Trichonisisa carbonate type, low conductivity lake (‘class II, lowsalinity’warm lake). Nitrogen and phosphorus concentrations were ratherlow.The inorganic nitrogen content fluctuated widely over the twoannual cycles examined. On the contrary, phosphorusconcentrationsshowed no significant changes. The limiting factor during1985–86was P, while N was limiting during stratification in 1988–89.Aweak correlation was found between the plankton communityfeatures(species abundance, biomass, chlorophyll-a) and lightpenetration. At present the eutrophication process fromoligotrophytowards mesotrophy has not been essentiallyaccelerated.

The show cave of Diros vs. wild caves of Peloponnese, Greece - distribution patterns of Cyanobacteria

*aamilli@biol.uoa.gr 2011). Under such conditions the oligotrophic nature of cave environments is expected to change through organic inputs that alter both the food web, and the abundance and distribution of cave organisms (Hoyos et al., 1998; Fernández-Cortés et al., 2006; Saiz-Jimenez et al., 2011; Saiz-Jimenez, 2012). Additionally, the artificial lighting system in the show caves affects the photosynthetic microflora in areas around the installed illumination equipment. The photosynthetic community thriving in proximity to artificial lighting is known as ‘Lampenflora’– a term introduced by Dobàt (1963) – and it was first studied in Austrian caves (Kyrle, 1923; Morton and Gams, 1925). Further research has shown that the growth and distribution of these floristic aggregations depend on abiotic factors such as light quality and intensity, temperature, relative humidity, as well as type and coherence of the underlying substratum (Roldán et INTRODUCTION

TRANSFER OF AMPHORA EULENSTEINII GRUNOW TO THE GENUS SEMINAVIS D. G. MANN

The taxonomie status of the species Amphora eulensteinii Grunow is at present insufficiently known. The study of morphology and fine structure of this species, discovered in core samples from Rhode Island, revealed that it is characterized by the presence of lineolate, slitlike areolae, a dorsally widened axial area and a ventrally displaced raphe that runs internally on a dorsally bended silica rib. All of these structures together with the shape of the valve clearly place this species in the genus Seminavis as it was established by Mann (in Round et al. 1990). The lack of verified original material has led to the designation of a neotype for Seminavis eulensteinii (Grunow) Danielidis, Ford & Kennett comb. nov.